This application is based on and claims priority under 35 U.S.C. xc2xa7 119 with respect to Japanese Application No. 2001-041629 filed on Feb. 19, 2001, the entire content of which is incorporated herein by reference.
This invention generally relates to a hydraulic brake apparatus for a vehicle. More particularly, this invention pertains to a vehicle hydraulic brake apparatus provided with an auxiliary hydraulic pressure source and a master cylinder having a master piston, with the master piston being driven by power hydraulic pressure supplied from the auxiliary hydraulic pressure source.
There are a variety of known vehicle hydraulic brake apparatus, one of which is disclosed in U.S. Pat. No. 6,135,577 (corresponding to Japanese Patent Laid-Open Publication No. 11-34859). This patent describes a vehicle hydraulic brake apparatus employing a pump operation control apparatus. The pump operation control apparatus is adapted to operate a pump (an auxiliary hydraulic pressure source) in response to each braking operation of a brake operating member and to release the pump after a predetermined time has elapsed or in response to a release of the brake operating member. Therefore, the pump operation control apparatus can always maintain an accumulator pressure at a predetermined pressure level.
More specifically, when a brake switch has been switched on, the operation of the pump is started. After the predetermined time has elapsed from the moment at which the brake switch has been switched on, the operation of the pump is interrupted. If the brake switch is continuously switched on after the predetermined time has elapsed, the pump is operated for a time extended from the predetermined time until the brake switch is switched off. If the brake switch is again switched on before the predetermined time elapses, the pump is operated until the predetermined time elapses from the moment at which the brake switch has again been switched on.
U.S. Pat. No. 5,498,070 (corresponding to Japanese Patent Publication No. 2849972) describes a fluid pressure boosting type brake system that is designed to drive a fluid pump (an auxiliary hydraulic pressure pump) in accordance with the consumption of fluid pressure in a brake device and reliably ensure sufficient fluid pressure in a fluid pressure source. The fluid pump is adapted to be driven in response to a pressure value detected by a pressure detector when the pressure detector is in a normal state. On the other hand, should the fluid pump not be controlled based upon the detected pressure value by the pressure detector, the fluid pump can be driven in response to the consumption of the fluid pressure corresponding to the braking operation. For example, should the fluid pump not be controlled based upon the detected pressure value by the pressure detector, the fluid pump can be driven on and off for each preset time with a predetermined period while the braking operation has been performed.
Considering the pump operation control apparatus disclosed in U.S. Pat. No. 6,135,577 and Japanese Patent Laid-Open Publication No. 11-34859, the pump is operated for the predetermined time after the braking operation is detected, i.e., after the brake switch was switched on. Therefore, the accumulator pressure may be increased excessively. To overcome this drawback or prevent the occurrence of such a possibility, the operation of the pump is interrupted when a relief valve is operated, when the electric current of the motor for operating the pump becomes equal to or above a predetermined value, or when the number of revolutions of the motor becomes equal to or below a predetermined value. However, this requires a mechanism for detecting the electric current or for detecting the number of revolutions, or other similar devices, thus leading to an increase in the number of components.
With respect to the fluid pressure boosting type brake system disclosed in U.S. Pat. No. 5,498,070 and Japanese Patent Publication 2849972, the fluid pump is operated on and off so that the fluid pressure in the fluid pressure source may be excessively increased or sufficient fluid pressure may not be ensured in the fluid pressure source. Further, the method used to estimate the consumption of the fluid pressure corresponding to the braking operation may not be accurately performed due to, for example, the road surface condition.
Accordingly, the pump operation control apparatus and the fluid pressure boosting type brake system are still susceptible of certain improvements with respect to appropriately controlling the operation of the auxiliary hydraulic pressure source to decrease the load applied to the auxiliary hydraulic pressure source.
A hydraulic brake apparatus for a vehicle includes a brake operating member, a master cylinder including a master piston which is movable in the forward direction in response to the depressing operation of the brake operating member for pressurizing brake fluid in a reservoir and outputting a master cylinder hydraulic pressure to a wheel brake cylinder mounted on a vehicle wheel in response to the movement of the master piston in the forward direction, and an auxiliary hydraulic pressure source for pressurizing the brake fluid in the reservoir to a first predetermined pressure level and for outputting a power hydraulic pressure. The hydraulic brake apparatus also includes a regulating means, a hydraulic pressure detecting means, and a control means.
The regulating means is connected with the auxiliary hydraulic pressure source and the reservoir for regulating the power hydraulic pressure outputted from the auxiliary hydraulic pressure source to a second predetermined pressure level for driving the master piston by the regulated power hydraulic pressure, and for terminating the regulating operation when the regulated hydraulic pressure becomes equal to a reaction force of the master cylinder relative to the master piston. The hydraulic pressure detecting means detects the master cylinder hydraulic pressure. The control means compares the master cylinder hydraulic pressure detected by the hydraulic pressure detecting means with a predetermined pressure value, implements operation of the auxiliary hydraulic pressure source when the depressing operation of the brake operating member is judged in a stage where the detected master cylinder hydraulic pressure is above the predetermined pressure value, and terminates operation of the auxiliary hydraulic pressure source when the master cylinder hydraulic pressure detected by the hydraulic pressure detecting means is stabilized at an approximately fixed pressure value after being increased. The regulating means is preferably in the form of a hydraulically actuated booster device.
The hydraulic pressure detecting means detects the master cylinder hydraulic pressure every fixed predetermined period of time, and the control means compares the difference between the master cylinder hydraulic pressure detected by the hydraulic pressure detecting means at a previous time and the master cylinder hydraulic pressure detected by the hydraulic pressure detecting means at a present time with a predetermined value. The operation of the auxiliary hydraulic pressure source is terminated when the difference is maintained below the predetermined value for a predetermined period of time or more than that.
According to another aspect, the hydraulic brake apparatus for a vehicle includes a brake operating member, a master cylinder including a master piston which is movable in the forward direction in response to the depressing operation of the brake operating member for pressurizing brake fluid in a reservoir and outputting a master cylinder hydraulic pressure to a wheel brake cylinder mounted on a vehicle wheel in response to movement of the master piston in the forward direction, and an auxiliary hydraulic pressure source for pressurizing the brake fluid in the reservoir to a predetermined pressure level and for outputting a power hydraulic pressure. The hydraulic brake apparatus also includes master piston driving means, linear solenoid valve means, control means, and hydraulic pressure detecting means.
The master piston driving means drives the master piston with the power hydraulic pressure outputted from the auxiliary hydraulic pressure source, while the linear solenoid valve means controls the power hydraulic pressure supplied to the master piston driving means from the auxiliary hydraulic pressure source. The control means performs an operation control of the linear solenoid valve means based upon predetermined electric current regardless of the depressing operation of the brake operating member and performs an auto-braking control by adjusting the master cylinder hydraulic pressure. The hydraulic pressure detecting means detects the master cylinder hydraulic pressure. The control means operates the auxiliary hydraulic pressure source when the auto-braking control is performed and terminates operation of the auxiliary hydraulic pressure source when the master cylinder hydraulic pressure detected by the hydraulic pressure detecting means is maintained at an approximately fixed pressure value after being increased.
The auto-braking control includes at least one of a brake steering control for restraining an oversteer or an understeer of the vehicle, a traction control for restraining an acceleration slip of a driving wheel when the vehicle is accelerated, a vehicle distance control for controlling a vehicle distance from the vehicle towards a forward running vehicle and a down-hill control for controlling a vehicle speed to be a predetermined vehicle speed during the vehicle running on the down-hill.
Preferably, the hydraulic pressure detecting means detects the master cylinder hydraulic pressure every fixed predetermined period of time. The control means compares the difference between the master cylinder hydraulic pressure detected by the hydraulic pressure detecting means at a previous time and the master cylinder hydraulic pressure detected by the hydraulic pressure detecting means at a present time with a predetermined value, and terminates operation of the auxiliary hydraulic pressure source when the difference is maintained below the predetermined value for a predetermined period of time or more than that.
According to a further aspect, a method hydraulic braking for a vehicle involves pressurizing brake fluid in a reservoir through forward movement of a master piston in a master cylinder in response to a depressing operation of the brake operating member to output a master cylinder hydraulic pressure to a wheel brake cylinder mounted on a vehicle wheel, detecting the master cylinder hydraulic pressure, pressurizing the brake fluid in the reservoir to a first predetermined pressure level through operation of an auxiliary hydraulic pressure source to output a power hydraulic pressure, regulating the outputted power hydraulic pressure to a second predetermined pressure level to produce a regulated power hydraulic pressure and terminating regulation of the power hydraulic pressure when the regulated hydraulic pressure becomes equal to a reaction force of the master cylinder relative to the master piston, driving the master piston with the regulated power hydraulic pressure, comparing the detected master cylinder hydraulic pressure with a predetermined pressure value, operating the auxiliary hydraulic pressure source when depression of the brake operating member is judged to be in a stage in which the detected master cylinder hydraulic pressure is greater than the predetermined pressure value, and terminating operation of the auxiliary hydraulic pressure source when the detected master cylinder hydraulic pressure is stabilized at a substantially fixed pressure value after being increased.
The operation control of the auxiliary hydraulic pressure source can be relatively easily and appropriately performed by the hydraulic pressure detecting means. Therefore, there is no need to provide an additional detecting means. Further, the load applied to the auxiliary hydraulic pressure source can be decreased.